It is known that when a symmetric loaad is applied to the secondary side of a transformer, or when the secondary side has no load thereon, for example when the transformer idles, the magnetizing current required to sustain magnetization of the transformer core obtains the form of brief current pulses occurring periodically in dependence on the A.C. voltage applied, wherewith two mutually sequential current pulses of brief duration are substantially symmetrical in relation to a zero level.
It is also known that when a transformer is loaded asymmetrically on its secondary side, i.e. when current is taken from the secondary side of the transformer in solely one predetermined direction while current in the other direction is blocked by a device through which current can flow in solely one direction, e.g. a D.C. rectifier, that the magnetizing current through the transformer will have an asymmetric form, and in particular that each alternate current pulse will have an extremely high amplitude, while each other or intermediate pulse will have a considerably reduced amplitude. This also applies to the case of an asymmetric primary voltage.
It has also been established earlier that the time positions of the magnetizing current pulses appear at the zero-crossing points of the primary A.C. voltage, both when the load is symmetrical and asymmetrical.
It is also known that an asymmetric load which is constant in time can be balanced with the aid of a diode arrangement on the primary side, although this solution is not successful when the load varies. It is also known that overheating of the transformer, due to a high magnetizing current, can be avoided with the aid of electrical devices connected in series, e.g. resistors or inductances incorporated in the primary circuit, although this solution does not enable the transformer to be utilized to the full and normally significant energy losses are experienced in the series-connected devices.